624 Hektor is the largest

Jupiter trojan The Jupiter trojans, commonly called trojan asteroids or simply trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange p ...

and the namesake of the Hektor family, with a highly elongated shape equivalent in volume to a sphere of approximately 225 to 250 kilometers diameter. It was discovered on 10 February 1907, by astronomer

August Kopff August Kopff (February 5, 1882 – April 25, 1960) was a German astronomer and discoverer of several comets and asteroids. Kopff studied and worked in Heidelberg, getting his PhD there in 1906 and he then joined the Humboldt University of Berli ...

Heidelberg Observatory Heidelberg (; Palatine German: ') is a city in the German state of Baden-Württemberg, situated on the river Neckar in south-west Germany. As of the 2016 census, its population was 159,914, of which roughly a quarter consisted of student ...

in southwest Germany, and named after the Trojan prince

Hector In Greek mythology, Hector (; grc, Ἕκτωρ, Hektōr, label=none, ) is a character in Homer's Iliad. He was a Trojan prince and the greatest warrior for Troy during the Trojan War. Hector led the Trojans and their allies in the defense o ...

, from Greek mythology. It has one small 12-kilometer sized

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...

, Skamandrios, discovered in 2006.

Description

''Hektor'' is a

D-type asteroid D-type asteroids have a very low albedo and a featureless reddish spectrum. It has been suggested that they have a composition of organic-rich silicates, carbon and anhydrous silicates, possibly with water ice in their interiors. D-type asteroids ...

, dark and reddish in colour. It lies in Jupiter's leading

Lagrangian point In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of t ...

, , called the Greek camp after one of the two sides in the legendary

Trojan War In Greek mythology, the Trojan War was waged against the city of Troy by the Achaeans ( Greeks) after Paris of Troy took Helen from her husband Menelaus, king of Sparta. The war is one of the most important events in Greek mythology and ...

. Hektor is named after the Trojan hero

Hektor In Greek mythology, Hector (; grc, Ἕκτωρ, Hektōr, label=none, ) is a character in Homer's Iliad. He was a Trojan prince and the greatest warrior for Troy during the Trojan War. Hector led the Trojans and their allies in the defense o ...

and is thus one of two trojan asteroids that is "misplaced" in the wrong camp (the other one being 617 Patroclus in the

Trojan camp This is a list of Jupiter trojans that lie in the Trojan camp, an elongated curved region around the trailing Lagrangian point, 60° behind Jupiter. All the asteroids at the trailing point have names corresponding to participants on the Trojan ...

Contact-binary hypothesis

Hektor is one of the most elongated bodies of its size in the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

, being approximately 403 km in its longest dimension, but averaging only around 201 km in its other dimensions, with a total volume equivalent to an approx 250 km diameter sphere, and an estimated mass of (thus density of 1.0g/cm³). It is thought that Hektor might be a

contact binary In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overcontac ...

(two asteroids joined by gravitational attraction) like

216 Kleopatra 216 Kleopatra is a large M-type asteroid with a mean diameter of and is noted for its elongate bone or dumbbell shape. It was discovered on 10 April 1880 by Austrian astronomer Johann Palisa at the Austrian Naval Pola Observatory, in what is no ...

, composed of two more rounded lobes of 220 and 183 km mean diameters.

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

observations of Hektor in 1993 did not show an obvious bilobate shape because of a limited

angular resolution Angular resolution describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object, thereby making it a major determinant of image resolut ...

. On 17 July 2006, the Keck 10-meter-II-telescope and its laser guide star

adaptive optics Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical tele ...

(AO) system indicated a bilobate shape for Hektor, which was reinforced by later studies that, together with multiple historical lightcurves, suggest a rotation period of 6.9205 hours. Hektor is, so far, one of only four known binary trojan asteroids in the point (the others being 16974 Iphthime, 3548 Eurybates, and

15094 Polymele 15094 Polymele is a primitive Jupiter trojan from the Greek camp, approximately in diameter. It is a target of the ''Lucy'' mission with a close flyby planned to occur in September 2027. It was discovered on 17 November 1999, by astronomers wi ...

) and the first known trojan with a satellite companion.

617 Patroclus 617 Patroclus ( ) is a large binary Jupiter trojan asteroid. It is a dark D-type asteroid and a slow rotator, due to the 103-hour orbital period of its two components. It is one of five Jovian asteroids targeted by the ''Lucy'' space probe, and ...

, another large trojan asteroid located in the point, is composed of two almost equal-sized components. There are now a further two known binary asteroids in the L5 point, (17365) 1978 VF11 and 29314 Eurydamas.

Satellite

A 10–15-km-diameter moon, named Skamandrios, was detected orbiting 624 Hektor in 2006 with a semi-major axis of 623.5 km and an orbital period of 2.9651 days (71.162 hours). It was confirmed with Keck observations in November 2011, and was then named on 12 March 2017. No mass estimate was provided, but the equivalent volume suggests an approximate mass of if the two bodies are of the same density. Its orbit is highly inclined and eccentric, and it is likely that its rotation is chaotic. Marchis et al. (2014) speculate that it was ejected after a low-velocity collision produced the bilobed primary. The newly merged primary could have spun fast enough to be unstable and shed some mass. The dynamics of Skamandrios can be modeled by the restricted four-body problem.

Studies

624 Hektor was in a 2003 study of asteroids using the Hubble FGS. Asteroids studied include

63 Ausonia Ausonia (minor planet designation: 63 Ausonia) is a stony Vestian asteroid from the inner region of the asteroid belt, approximately 100 kilometers (60 miles) in diameter. It was discovered by Italian astronomer Annibale de Gasparis on 10 Februar ...

15 Eunomia Eunomia (minor planet designation 15 Eunomia) is a very large asteroid in the inner asteroid belt. It is the largest of the stony ( S-type) asteroids, with 3 Juno as a close second. It is quite a massive asteroid, in 6th to 8th place (to within ...

, 43 Ariadne,

44 Nysa Nysa (minor planet designation: 44 Nysa) is a large and very bright main-belt asteroid, and the brightest member of the Nysian asteroid family. It is classified as a rare class E asteroid and is probably the largest of this type (though 55 Pan ...

, and 624 Hektor. It has since been revisited several times, particularly as a test of the upgraded resolution of the Keck Observatory's LGS Adaptive Optics system which allowed Earth-based observation of binary asteroids for the first time. The asteroid has also been imaged by the

NEOWISE Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and SMEX-6) is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 201 ...

and

AKARI Akari (ASTRO-F) was an infrared astronomy satellite developed by Japan Aerospace Exploration Agency, in cooperation with institutes of Europe and Korea. It was launched on 21 February 2006, at 21:28 UTC (06:28, 22 February JST) by M-V rocke ...

all-sky studies, which reported highly divergent size estimates of 147.4 and 231.0 kilometers respectively, although this mostly arises from large differences in estimated

albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...

(approximately 0.107 for NEOWISE, and a much lower 0.034 for AKARI) rather than its

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it ...

being measured only briefly at opposing extremes of a widely varying cycle such as thought to account for the uncertainty over the size of 1173 Anchises (624 Hektor's own abs. mag. recorded as a relatively similar 7.20 and 7.49 by the two studies). It is, unusually, not included in the published

IRAS The Infrared Astronomical Satellite ( Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten ...

results, and is therefore the largest Jupiter trojan to be omitted from that study.

References

External links

Keck image of Hektor and moon
(Marchis 2011-Nov-11)
Distant Asteroid Revealed to be a Complex Mini Geological World
(2014 February 27)

Robert Johnston, johnstonsarchive.net * * {{DEFAULTSORT:Hektor 000624 000624 Discoveries by August Kopff Named minor planets 000624 000624 000624 19070210